#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int64_t N;
  cin >> N;
  auto f = [](int64_t x) {
    int64_t res = 0;
    while (x > 0) {
      res += x % 10;
      x /= 10;
    }
    return res;
  };
  for (int i = 0; i < 99; i++) {
    N = f(N);
  }
  cout << N << '\n';
  return 0;
}